This specification relates to enhancing speech understanding, particularly in individuals with cochlear implants who possess limited residual acoustic hearing.
Individuals with residual hearing restricted to the low frequencies (below about 500 Hz-750 Hz) have been implanted with a relatively short electrode array designed to preserve as much of the residual hearing as possible in the apical region. These individuals, in addition to full-insertion implant users who have some residual hearing in the unimplanted ear, have the potential to combine the electric and acoustic sources of information. For both simulated and real implant processing, the addition of low frequency acoustic stimulation often enhances speech understanding, particularly when listening to speech in the presence of competing speech. The benefit of this electric-acoustic stimulation (EAS) occurs even when the acoustic stimulation alone provides little or no intelligibility.
It has been suggested that listeners combine the relatively weak pitch information conveyed by the electric stimulation with the strong pitch cue from the target talker's fundamental frequency (F0) or voice pitch in the low-frequency acoustic region to segregate target and background. Further, it has been found that F0 aids in the segregation of competing talkers and that mean F0 differences between target and masker aid speech understanding with EAS, but not with electrical stimulation alone. F0 has also been shown to likely play an important role independent of any role that the first formant may play: the addition to vocoder stimulation of 300-Hz low-pass speech improved speech intelligibility in a competing background.